Prediction and interpretation of rates of hypolimnetic oxygen depletion

The areal hypolimnetic oxygen deficit model (AHOD) developed by Strom (1931) and Hutchinson (1938) was tested by examining the predictions which the model makes and by testing the assumptions which were made during the formulation of that model. The model was found to be incorrect. Rates of hypolimnetic oxygen depletion are strongly influenced by the morphometry and temperature of the hypolimnion. Lake morphometry influences at least two processes which affect oxygen concentrations. Significantly more oxygen is turbulently transferred into the hypolimnia of shallow lakes than deep lakes. However the maximum rates of vertical transport are always less than 15% of the observed rate of oxygen depletion. The morphometry of the hypolimnion exerts a much stronger influence upon the amount of respiration which occurs within the hypolimnetic water column. The amount of respiration measured in the water column increases as the thickness of the hypolimnetic water column increases. In oligotrophic lakes with shallow hypolimnia, less than 20% of the total amount of oxygen consumed in the hypolimnion is respired in the water column. In deep lakes more than 60% of the total amount of oxygen consumed is respired within the water column. Measured rates of water column respiration are strongly correlated with the temperature and amount of particulate organic matter present in the water column.The rate of oxygen consumption within the hypolimnion is constant throughout the period of thermal stratification. Respiration does not depend upon the ambient concentration of oxygen present within the hypolimnion. Changes in oxygen concentration within any stratum of the hypolimnion of a lake can be predicted from a knowledge of the retention of phosphorus by the lake's sediments (Rp), the average temperature of the stratum during the period of thermal stratification (T), and the ratio of the volume of the stratum to the area of lake sediments horizontally contiguous to the stratum (V:SA). A simple statistical model developed from published estimates of rates of oxygen consumption (VOD mg/m('3)/day) predicts thatVOD = -6.6 + .0081T*Rp + 11.07T - 2.32T*Ln(V:SA).The predictions of this equation agree very well with rates of oxygen depletion measured in 12 lakes which possess a diversity of physical and chemical characteristics. During the period of stratification, hypolimnetic oxygen concentrations can be estimated from the predicted rate of oxgyen depletion and an estimate of the initial oxygen concentration within the hypolimnion at the onset of stratification